1. Field of the Invention
The present invention relates to a charging member for charging a material to be charged by contacting the charging member to which a voltage is impressed to the material, and the method of the manufacture thereof, and an electrophotographic apparatus using the charging member.
2. Related Background Art
In image forming apparatuses such as an electrophotographic apparatus (e.g. a copying machine and a printer), and an electrostatic recorder, a corona discharging device, which is a non-contact charging system, has conventionally been used as a charging means for image carriers such as electrophotographic photosensitive members and electrostatic-recording dielectrics, which are materials to be charged.
Although the corona discharging device has advantages such as excellent uniformity of charging, it requires an expensive high voltage source. It also requires a large space for itself and for shielding the high-voltage source. It produces a relatively large quantity of products formed by corona, such as ozone, which require additional means and mechanisms for the treatment of such products, leading to increasing in equipment size and cost.
Recently, charging means using a contact charging system has been used instead of corona charging devices. Contact charging is used for charging the surface of a material to be charged to a predetermined polarity and potential by contacting a charging member to which a voltage is impressed with a material to be charged, and can lower the voltage of the power source. Contact charging has such advantages as decrease in the quantity of products formed by corona, and the simplification and cost reduction of the equipment.
A contact charging member is generally formed by the following methods:
A) A method in which a conductive elastic layer is formed along a metallic conductive base material (core metal), and the conductive elastic layer is in turn coated with a thin resistive layer and a thin surface layer along the periphery thereof by dipping or roll coating.
B) A method in which a seamless tube is formed from a fluorinated resin, utilizing its non-adhesive and non-contaminating properties, the inner diameter of the seamless tube is formed to be smaller than the thickness of the conductive elastic layer, and the conductive elastic layer is pushed in the seamless tube; or a method in which a shrinking (heat shrinking) seamless tube formed from a fluorinated resin, which is heated to shrink and form a surface layer.
However, the method A) has the following problems:
1) Since the material for each layer must be dissolved in an organic solvent to form a paint, the material type is limited. (Unless the solubility factor of each layer is changed, the layers dissolve each other and the operation of the layers are degraded.)
2) Since the lower layer (resistive layer) is dried before the upper layer is applied and dried, productivity is low.
3) Since solubility factors differ, the adhesion of each layer is low, and may cause floating or wrinkles to occur. Also, since a primer is often used for improving adhesion, the costs are elevated.
4) The thickness of each layer is uneven, and it is difficult to finish the surface to be flat and smooth.
5) Especially when a foamed material is used for a supporting member, the image is affected by the unevenness of the surface causing defective images.
The method B) also has the following problems:
1) It is difficult to disperse conductive pigments uniformly in a fluorinated resin.
2) The fluorinated resin itself is expensive.
3) Since the fluorinated resin has poor adhesion properties, the internal surface of the tube must be etched, resulting in high costs.
4) Since the fluorinated resin is hard, the surface hardness of the charging roller becomes high, and the developer may be fused on the surface of the photosensitive member.
5) Since the fluorinated resin is difficult to undergo elastic deformation, the tube may break or become eccentric due to a large force produced on joining.